1. Field of the Invention
The present invention relates to an eye measuring apparatus and method and, more particularly, to an eye measuring apparatus and method having an automatic fogging producer for effectively relaxing accommodation of visual acuity.
In an optometric apparatus for automatically measuring the refracting power of an eye to be examined, i.e., in a so-called objective eye refracting power measuring apparatus, it is necessary to perform a measurement of the refracting power while the eye to be examined is fixed and relaxed. For this purpose, there has been provided an eye refracting power measuring apparatus having an automatic fogging producer which realizes a state in which an eye to be examined is reliably relaxed (e.g., Japanese Patent Publication No. 62-44489 or 63-6012 (U.S. Pat. No. 4,431,278)).
In this eye refracting power measuring apparatus having the conventional automatic fogging producer of the above sort, a feedback system is constituted by the fogging producer for moving the position of the image of a target with a predetermined shape along the direction of optical axis of an eye to be examined, and a refracting power detector for measuring the refracting power of the eye to be examined. This apparatus further includes a position detector for outputting an alignment signal when the apparatus main body is in a position at which the refracting power of the eye to be examined is measurable, and a devices for activating the feedback system in accordance with this alignment signal. The automatic fogging producer whose feedback system is constituted by the refracting power detector and the fogging producer is arranged such that the fogged state of the target is changed in correspondence with the output from the refracting power detector. That is, since it is possible to detect the refractive state of an eye to be examined and reflect the detection result on the position of the target, the image of the target can be moved in a direction in which the eye to be examined is relaxed.
In this conventional apparatus with the above arrangement, if alignment between an eye to be examined and the apparatus main body is performed even momentarily, the refractive state of the eye in one meridian direction inherent in the apparatus is measured automatically (to be referred to as a preliminary measurement hereinafter). In accordance with the refractive state thus preliminarily measured, the image of the target is initially positioned slightly before the retina of the eye to be examined, i.e., in a direction in which the eye attempts to focus on a far point. Subsequently, when an alignment signal is detected, the fogging producer automatically operates such that the eye to be examined attempts to focus on the far point at any instant. After this automatic fogging operation is repeatedly executed, it is confirmed that the alignment is stably performed and the preliminarily measured refractive state is stabilized, and the refracting power of the eye is normally measured for all meridians.
To accurately measure the refracting power while the eye to be examined is in a relaxed state, the above operation is simply repeated for several cycles, thereby performing the normal measurement for the refracting power in all meridian directions of the eye a plurality of times.
As described above, in the eye refracting power measuring apparatus having the conventional automatic fogging producer, the normal measurement for the refracting power of an eye to be examined is merely repeated independently a plurality of times. Therefore, the preceding normal measurement value is not at all reflected on the subsequent automatic fogging operation. In other words, the automatic fogging operation depends on only the preliminary measurement value of refracting power measured in a predetermined meridian direction inherent in the apparatus. For this reason, in a common eye refracting power measuring apparatus in which the astigmatic information of an eye to be examined cannot be obtained unless the eye refracting power is normally measured in all meridian directions, it is impossible to perform an automatic fogging operation which takes account of the astigmatic information of an eye to be examined.
For example, the focal range of an eye to be examined having a spherical power (spherical degree) S and a cylindrical power (astigmatic degree) C is present between a position corresponding to the spherical power S and a position corresponding to the sum total S+C of the spherical power and the cylindrical power. If, therefore, the cylindrical power C is large and a predetermined meridian direction of a preliminary measurement is close to a meridian direction corresponding to the maximum refracting power of an eye to be examined, a target which is supposed to be moved farther than the far point of the eye finally exists within the focal range of the eye in some cases. This may prolong the fogging operation time, and there is also a possibility that the automatic fogging operation is finished before the eye to be examined relaxes sufficiently.
In addition, when the facts that different patients have different angles of astigmatism axes and the measurement meridian direction for the preliminary measurement is inherent in an apparatus are taken into consideration, the same automatic fogging operation may be performed for patients having largely different cylindrical powers rather than patients having the same cylindrical power.
As described above, in the eye refracting power measuring apparatus having the conventional automatic fogging producer, the degree of astigmatism of an eye to be examined is not taken into account at all in the automatic fogging operation. Therefore, for an eye to be examined with a large cylindrical power, the fogging operation becomes time-consuming, and relaxation of the eye is also insufficient.
Recently, an eye measuring apparatus has been developed which can continuously measure the refracting power and the corneal shape of an eye to be examined. In such an eye measuring apparatus, so-called an autorefkeratometer which is a combination of an eye refracting power measuring apparatus (refractometer) and a corneal shape measuring apparatus (keratometer), it is necessary to perform a refracting power measurement while an eye to be examined is fixed and relaxed. For this purpose, as disclosed in Japanese Patent Publication No. 4-31690, there has been provided an eye measuring apparatus having an automatic fogging producer which realizes a state in which an eye to be examined is stably relaxed.
When a measurement of the eye refracting power is to be performed by the above eye measuring apparatus having the conventional automatic fogging producer, a target is set in a fogged state, and the refracting power is measured while an eye to be examined is fixed and relaxed. Subsequently, in a measurement of the corneal shape, the target is positioned by referring to the measured eye refracting power such that the target is clearly seen by the eye to be examined, and the corneal shape is measured while the eye is forced to gaze steadily at the center of the target.
In an eye measuring apparatus having an automatic fogging producer, measurements of the refracting power and the corneal shape of an eye to be examined are generally performed a plurality of times in order to avoid an erroneous measurement in a condition in which fixation and relaxation of the eye are unsatisfactory, and to improve the accuracy of measurement values. In the above conventional eye measuring apparatus, however, in a measurement of the corneal shape, the target is so positioned as to be clearly seen by an eye to be examined, and the eye is forced to gaze steadily at the center of the target. Therefore, the eye to be examined readily falls into a visual acuity accommodation state. Consequently, the influence of the accommodation of visual acuity remains in a measurement of the eye refracting power performed next to make the fogging operation time-consuming, and this makes it difficult to reliably measure an eye refracting power with a high accuracy.